Wireless digital data transmission from a passive transceiver

ABSTRACT

A wireless network transmits digital data. The network includes an active transceiver to transmit carrier waves at a succession of preselected frequencies and a transponder. The transponder transmits digital data to the active transceiver by partially reflecting the carrier waves.

BACKGROUND OF THE INVENTION

This invention relates to wireless digital data transmission.

Typical wireless digital data communication is affected betweenradio-frequency (RF) active transceivers contained in each of twocommunication devices. Each RF transceiver has a separate power sourceto produce the radio-frequency carrier waves used to transmit data tothe other devices.

SUMMARY OF THE INVENTION

In a first aspect, the invention provides a wireless network fortransmitting digital data. The network includes an active transceiver totransmit carrier waves at a succession of preselected frequencies and atransponder. The transponder transmits digital data to the activetransceiver by partially reflecting the carrier waves.

In a second aspect, the invention provides a transceiver for digitaldata. The transceiver includes an antenna to transmit radio-frequency(RF) carrier waves and an RF module coupled to drive the antenna toproduce the RF carrier waves. The RF module detects reflected portionsof the produced RF carrier waves at the same time. The RF carrier waveshave a succession of frequencies.

In a third aspect, the invention provides a method for wireless datatransmission. The method includes transmitting radio-frequency (RF)carrier waves to a transponder at a succession of frequencies andreceiving reflected portions of the RF carrier waves from thetransponder. The reflected portions are digitally modulated.

In a fourth aspect, the invention provides a method of wireless digitalcommunication. The method includes receiving a first radio-frequency(RF) carrier wave at a receiver, digitally modulating an RF reflectivityof the receiver, and reflecting a portion of the first RF carrier wavein response to the digitally modulating of the RF reflectivity. Themethod includes repeating the receiving, digitally modulating, andreflecting for a second RF carrier wave at a new frequency.

Other features and advantages of the invention will be apparent from thefollowing description and from the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an embodiment of a wireless network for digital dataexchanges;

FIG. 2A shows transceivers of the wireless network of FIG. 1;

FIG. 2B shows an alternate form for the antennae of the transponders ofFIGS. 1 and 2A;

FIG. 3 shows a method by which an active transceiver receives data fromtransponders of the network of FIG. 2A; and

FIG. 4 shows a method by which a transponder transmits data to theactive transceiver of FIGS. 2A-3.

DETAILED DESCRIPTION

FIG. 1 shows a local wireless radio-frequency (RF) network 4 fortransmitting digital data between a digital device 6 capable ofcommunicating data and other digital devices 8, 14 capable ofcommunicating data. The digital device 6 contains an interrogator 10,which controls communications between digital device 6 and the otherdevices 8, 14. Each of the other devices 8, 14 includes a passivetransponder 12, 16. The interrogator 10 is a master of wirelesscommunication over the passive transponders 12, 16, which arecommunication slaves.

Though the transponders 12, 16 are communications slaves of theinterrogator 10, devices 8, 14 may control some functions of the digitaldevice 6 through the wireless network 4. The wireless network 4 supportshalf duplex communications of digital data between any of thetransponders 12, 16 and the interrogator 10.

The interrogator 10 is an active radio-frequency (RF) transceiver ofdigital data. The active transceiver can transmit digital data to thetransponders 12, 16 on an RF carrier wave, e.g., using differentialphase shift keying (DPSK) modulation. The interrogator 10 can alsoselectively receive digital data from an RF carrier wave that has beenmodulated through DPSK by one of the transponders 12, 16. Though thetransponders 12, 16 can both transmit data to and receive data from theinterrogator 10, the transponders 12, 16 are not the source of the RFcarrier waves used to transmit digital data to the interrogator 10.

Instead, the transponders 12, 16 transmit digital data by passivelyreflecting a portion of an unmodulated RF carrier wave, which wastransmitted by the interrogator 10. The digital data appears as a DPSKmodulation on the back reflected portion of the carrier wave. The DPSKmodulation is produced by changing the transmitting transponder 12, 16between RF reflective and non-reflective states. DPSK may be aconvenient modulation scheme, because the transponders 12, 16 transmitdata through passive reflection. The interrogator 10 receives a portionof the back reflected RF carrier wave and demodulates the receivedportion to retrieve the digital data sent by the transmittingtransponder 12, 16.

Since the transponders 12, 16 do not produce the RF carrier wave used totransmit data, they can operate with lower power sources than active RFtransceivers. The transponders 12, 16 may use small, inexpensive, andlight “buttons” batteries 13 or solar cells 17 as power sources, becausethey do not have to generate the RF carrier waves. Some embodiments ofthe transponders 12, 16 can even extract enough energy from the receivedRF carrier waves, to power their internal circuits (not shown).

Small and lightweight power sources make the transponders 12, 16convenient for use in embodiments of the devices 8, 14, which havespecial functionalities. For example, the devices 8, 14 may be personalidentity badges, cellular phones, pagers, personal digital assistants,notebook computers, keyboards, or computer mice. The devices 6, 8, 14may also be heavier objects such as printers and facsimile machines.

Referring now to FIG. 2A, the interrogator 10 includes an RF module 18,transmission and reception antennae 20, 22, and a processor 24. The RFmodule 18 generates a variable frequency voltage for driving the antenna20 to generate RF carrier waves. The RF module 18 also provides forvariable frequency filtering of RF radiation received by the antenna 22.The processor 24 contains logic for controlling the RF module 18 duringsignal transmission and reception. The processor 24 contains memory 25and logic elements 27 and may perform more complex activities, e.g.,database look ups, calculations, printing.

Some embodiments of the interrogator 10 use the same antenna for bothtransmitting and receiving RF signals

Each transponder 12, 16 includes an RF module 28, 30, an antenna 32, 34,a switch 36, 38, and a processor 40, 42. The RF modules 28, 30 controldata transmission modes of the associated antenna 32, 34 through theassociated switch 36, 38. The RF modules 28, 30 also provide variablefrequency filtering of RF radiation received by the associated antenna32, 34. The transponders 16 has separate antennas 34, 35 fortransmitting data to and receiving data from the interrogator 10. Theprocessors 40, 42 control the associated RF module 28, 30 and containboth memory 41, 43 and logic elements 45, 47 to provide for control ofdata transmission and reception.

The dimensions of the antennae 32, 34 provide good reflection of the RFradiation transmitted by the interrogator 10 when in a reflective state.The antennas 32, 34 have two states. In the closed state, the switch 36,38 shorts an electrical dipole loop through the associated antenna 32,34, i.e., forming a closed loop. The dipole loop partially back reflectsRF radiation, e.g., an RF carrier wave transmitted by the interrogator10. The interrogator 10 receives detectable amounts of back reflected RFradiation when the antennae 32, 34 are in the closed state. In the openstate, the switch 36, 38 does not close an electrical dipole loopthrough the associated antenna 32, 34. Then, the antennae 32, 34 reflectvery little RF radiation transmitted by the interrogator 10, e.g., theabove-mentioned RF carrier wave. The interrogator 10 does not receivedetectable amounts of back reflected RF radiation when the antennae 32,34 are in the open state.

The switches 36, 38 function at high enough frequencies so that thetransponders 12, 16 can transmit data at high bit rates. High frequencyswitches 36, 38 may be formed by single transistors, which series coupleacross the associated antenna 32, 34 to form an electrical dipole loop.The opened or closed state of the dipole loops are controlled by theassociated RF module 28, 30 through a gate bias or base current of thetransistor forming the switch 36, 38. Opening and closing the switches36, 38 modulates the reflectivity of the associated transponder 12, 16to an RF carrier wave received from the interrogator 10. Opening andclosing one of the switches 36, 38 in rapid succession produces areflected wave with a binary amplitude modulation at frequencies betweentens of kilo-Hertz and about a few mega-Hertz. The modulation phase isdetectable by the interrogator 10 at distances between about 10centimeters and 10 meters and provides for digital data transmission fornetwork 4. The detection distance depends on the transmit power leveland the reception gain of the interrogator 10.

Though the RF modules 28, 30 power the switches 36, 38 and any internallogic and/or memory, they do not produce the RF carrier waves that carrydata transmissions. The high energy costs for producing the RF carrierwaves used for data transmissions, in both directions, are born by theinterrogator 10. Thus, the RF modules 28, 30 use less power to transmitdigital data than active RF transmitters (not shown). Lower powerconsumption to transmit data translates into lower demands on powersources.

The interrogator 10 also hops to a new RF driving frequency at regularintervals. Frequency hopping reduces interference from background RFsources 44, 46, because the background RF sources 44, 46 usually do notfrequency hop. Between frequency hops, the interrogator 10 transmits anRF carrier wave in a predetermined member of a set of narrow frequencybands.

FIG. 2B shows another reflective dipole antenna 64 for an alternateembodiment of the transponders 12, 16 of FIGS. 1 and 2A. The antenna 64includes two linear segments 65, 66 positioned in a linear end-to-endarrangement. The length of each segment 65, 66 is about equal to ¼ ofthe wavelength of the carrier wave produced by the interrogator 10.

The reflectivity of the dipole antenna 64 is controlled by a high speedswitch 67 connecting the two segments 65, 66 in a linear arrangement. AnRF module 68, e.g., one of the RF modules 28, 30 of FIG. 2A, operatesthe switch 67. In the open state, the switch 67 is electrically open andthe antenna 64 performs as two separate ¼-wavelength antennae. In theclosed state, the switch 67 is closed and the antenna 64 performs as asingle ½-wavelength antenna. A pair of ¼-wavelength antennae and a ½wavelength antenna have substantially different RF reflectivities. Thus,the antenna 64 has a different reflectivity in the open and closedstates.

Some embodiments of the network 4 comply with protocols of the BluetoothSpecial Interest Group, www.bluetooth.com, published Jul. 16, 1999. Theprotocols of the Bluetooth Special Interest Group are used with spreadspectrum technology transmissions occurring in 79 preselected narrow RFbands. The narrow RF bands are one mega-Hertz wide, adjacent and locatedin the range between about 2.402 and 2.480 giga-Hertz. In this range,the transceivers 12, 16 of FIGS. 1 and 2A can transmit about 10⁻³ to10⁻¹ watts of RF by passive reflection of a received RF carrier wave.

In the embodiments implementing the protocols of the Bluetooth SpecialInterest Group, the devices 6, 8, 14 hop to an adjacent narrow RF bandeach 80 milli-seconds. Each hop increases the transmission frequencyuntil the upper extreme of the frequency range is reached. From theupper extreme, the devices 6, 8, 14 return to the lowest narrow RF bandof the range, i.e, between 2.402 and 2.403 giga-Hertz.

Other embodiments hop between a pseudo-random succession of frequenciesin a predetermined frequency range. The succession of frequencies iscommunicated to the slave transponders 12, 16 by the interrogator 10.The succession of frequencies and/or timing information for the hops maybe security coded to maintain privacy using the pseudo-random frequencyhopping scheme.

In both types of frequency hopping, the RF modules 18, 28, 30 filter outRF carrier frequencies that the interrogator 10 does not transmit. Eachtransponder 12, 16 is assigned a temporal sequence of RF carrierfrequencies. The temporal sequences for the different RF modules 28, 30differ so that the interrogator 10 can communicate with the transponders12, 16 individually. The interrogator 10 transmits timing data thatenables the RF modules 28, 30, to synchronize filtering with theassigned RF frequency hopping.

FIG. 3 illustrates a wireless method 50 of receiving data transmissionsfrom a passive transponder of a wireless network. For example, thetransponders may be the transponders 12, 16 of the network 4 of FIGS. 1and 2. An active transceiver sends an RF protocol message to a targettransponder (step 52). In FIG. 2A, the active transceiver is theinterrogator 10.

The protocol message sets up a protocol for subsequent datatransmissions by the targeted transponder. The protocol message maycontain transmission parameters that identify the targeted transponderand the calling active transceiver, the RF carrier frequency, frequencyhopping data, encrypting codes, and timing data. While the protocolmessage is being sent, the active transceiver and the target transponderact like an ordinary wireless transmitter-receiver pair. The protocolmessage may also include data and/or queries to the target transponderthat request responses.

After sending the protocol message, the active transceiver transmits anunmodulated RF carrier wave to the transponder via the wireless network(step 54). The transponder reflects the unmodulated RF carrier wave toproduce a modulated RF wave carrying data back to the activetransceiver. The active transceiver receives a portion of the RF carrierwave reflected back by the transponder (step 56). The active transceiverbandpass filters and demodulates the received RF carrier wave toretrieve digital data transmitted by the target transponder (step 58).The active transceiver determines whether a preselected time has elapsed(step 60). The preselected time period may be based on number of datapackets or bytes received or on a counted time. If the preselected timehas not elapsed, the transceiver continues to transmit the unmodulatedcarrier wave (step 54).

If the preselected time has elapsed, the active transceiver and targettransponder reset their RF transmission frequencies to a new value,i.e., a frequency hop (step 62). After the frequency hop, the activetransceiver transmits an RF carrier wave with the new frequency to thetarget transponder (step 54). In the illustrated embodiment, the activetransceiver also transmits a new protocol message to the transponderprior to transmitting the new RF carrier wave (step 52). The newprotocol message informs the target transponder of the new transmissionfrequency and/or other information. In some embodiments, severaltransmission cycles at different frequencies terminate before thetransmission of a new protocol message.

FIG. 4 shows a method 70 by which a target transponder transmits digitaldata to the active transceiver. For example, the transponders and activetransceiver may be the transponders 12, 16 and the interrogator 10 ofFIG. 2A. The target transponder receives a protocol message from theactive transceiver (step 72). The target transponder demodulates thereceived protocol message and performs setup procedures in response todata therein (step 74). For example, the setup procedures may includedetermining whether the transponder is the target of the protocolmessage. The setup procedures may also include setting a passband forfrequency filtering and procedures to produce data requested by theactive receiver. At a time determined by the protocol message, thetransponder receives an unmodulated RF carrier wave from the activetransceiver (step 76).

The target transponder modulates its own RF reflectivity between RFreflective and non-reflective states to reflect a portion of the RFcarrier wave back to the active transceiver (step 78). The reflectedportion of the RF carrier wave transmits data back to the activetransceiver in the form of digital DPSK modulation. To modulate its RFreflectivity, the target transponder opens and closes the RF currentloop formed by its receiving antenna 32, 34 as was described above. Thetarget transponder again DPSK modulates its own reflectivity to reflecta portion of another RF carrier wave having a new carrier frequency(step 80). The reflected portion of the RF carrier wave at the newfrequency transmits additional data back to the active transceiver. Aportion of each reflected RF carrier wave is received and demodulated bythe active transceiver to retrieve the transmitted data.

Other embodiments are within the scope of the following claims.

What is claimed is:
 1. A wireless network comprising: an active transceiver to transmit a protocol message on a modulated carrier wave and to subsequently transmit carrier waves at a succession of preselected frequencies, wherein the protocol message includes data for the preselected frequencies; and a transponder to transmit digital data to the active transceiver by partially reflecting a first carrier wave having a first of the succession of preselected frequencies and to partially reflect a second carrier wave having a second of the succession of preselected frequencies prior to receiving a new protocol message from the active transceiver.
 2. The wireless network of claim 1 wherein the active transceiver to transmit the carrier waves at radio frequencies.
 3. The wireless network of claim 1, further comprising: a second transponder to transmit digital data to the active transceiver by partially reflecting carrier waves of a second succession, the active transceiver to transmit the second succession at preselected second frequencies.
 4. The wireless network of claim 1, wherein the transponder comprises an antenna and a switch coupled to short a dipole.
 5. The wireless network of claim 1, wherein the transponder comprises two antenna segments and a switch coupling the segments together linearly.
 6. The wireless network of claim 4, wherein the switch is capable of opening and closing at a frequency of at least tens of kilo-Hertz.
 7. The wireless network of claim 2, wherein the transceiver operates at frequencies between about 2.402 and 2.480 giga-Hertz.
 8. The wireless network of claim 1, further comprising: a first device coupled to the active transceiver; and a second device selected from the group consisting of a cellular phone, pager, personal digital assistant, notebook computer, keyboard, and a computer mouse, the second device coupled to the transponder to provide data exchanges with the first device.
 9. A transceiver for digital data, comprising: an antenna to transmit radio-frequency (RF) carrier waves; and a RF module coupled to drive the antenna to produce the RF carrier waves and to detect reflected portions of the produced RF carrier waves, the RF carrier waves having a succession of frequencies, the RF module further coupled to drive the antenna to produce a modulated carrier wave to transmit a first protocol message, the first protocol message including data for the succession of frequencies, the RF module further coupled to produce and detect carrier waves of at least two of the succession of frequencies prior to transmission of a second protocol message.
 10. The transceiver of claim 9, wherein the RF module filters out received RF radiation at frequencies outside of a passband surrounding the frequencies driving the antenna.
 11. The transceiver of claim 9, wherein the transceiver automatically hops to new transmission frequencies while transmitting the RF carrier waves.
 12. The transceiver of claim 9, wherein the transceiver is configured to transmit and receive frequencies in compliance with protocols of the Bluetooth Special Interest Group.
 13. The transceiver of claim 9, further comprising: one of a computer, a printer, and facsimile machine coupled to the RF module to receive digital transmissions received therein.
 14. An apparatus, comprising: a transponder having an RF reflectivity, the transponder to receive a first protocol message including data for a succession of predetermined RF frequencies, the transponder further to modulate the RF reflectivity in response to receiving carrier waves having at least two of the succession of predetermined RF frequencies prior to receiving a second protocol message.
 15. The apparatus of claim 14, wherein the transponder further comprises: an RF antenna having the RF reflectivity; a switch serially coupled across the antenna to form a circuit; and an RF module coupled to operate the switch to modulate the RF reflectivity.
 16. The apparatus of claim 15, wherein the RF module is capable of receiving data transmissions on RF carrier waves.
 17. The apparatus of claim 16, wherein the RF module transmits and receives frequencies complying with protocols of the Bluetooth Special Interest Group.
 18. The apparatus of claim 15, further comprising: one of a cellular phone, a pager, a personal digital assistant, a computer, a keyboard, and a computer mouse coupled to control the RF module.
 19. The apparatus of claim 15, further comprising: an identity badge coupled to control the RF module.
 20. A method of wireless data transmission, comprising: transmitting a first protocol message on a modulated radio-frequency (RF) carrier wave, the protocol message including data for a succession of frequencies for subsequent RF transmissions; transmitting RF carrier waves to a transponder having at least two of the succession of frequencies; and receiving reflected portions of the RF carrier waves from the transponder, the reflected portions being digitally modulated; transmitting a second protocol message on a modulated radio-frequency (RF) carrier wave, the protocol message including data for a second succession of frequencies for subsequent RF transmissions.
 21. The method of claim 20, wherein the reflected portions have binary phase modulations.
 22. The method of claim 20, wherein the receiving further comprises filtering out received RF radiation outside of passbands surrounding the frequencies.
 23. The method of claim 20, further comprising: demodulating the received portions of the reflected carrier waves to retrieve transmitted digital data.
 24. A method of wireless digital communication, comprising: receiving a protocol message at a receiver from an interrogator, the protocol message including data for a succession of frequencies for subsequent RF transmissions; performing a setup procedure for data transmissions in response to receiving the protocol message; receiving a first radio-frequency (RF) carrier wave from the interrogator; digitally modulating an RF reflectivity of the receiver; back reflecting a portion of the first RF carrier wave in response to the digitally modulating an RF reflectivity; and digitally modulating the RF reflectivity of the receiver to back reflect a second RF carrier wave having a new carrier frequency prior to receiving a new protocol message.
 25. The method of claim 24, wherein the digitally modulating comprises: electrically opening and closing a circuit, the circuit including a receiving antenna as a serial element.
 26. The method of claim 26, wherein the electrically opening and closing includes modulating a conductivity of a transistor which forms a serial link in the circuit. 